72 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



As the spermatocyte enters the prophase of the first maturation 

 division the centrosome, lying in contact with the cell membrane, 

 divides, and the two daughter centrosomes move apart (Figure 1) 



until they arrive at opposite 

 poles of the cell (Figure 2). 

 Although the centrosomes dur- 

 ing their migration seem to 

 influence to some degree the 

 form of the cell, this modifica- 

 tion in outline is not so promi- 

 nent as in the honey bee. The 

 nucleus continues to lie close 

 to that one of the centro- 

 somes which in the cells ot 

 the honey bee we have desig- 

 nated as the dista,! centrosome 

 (Figure 2, dst.). 



The stages immediately fol- 

 lowing this correspond strik- 

 ingly to those of the honey bee. 

 The chromatin, after passing 

 through a spireme condition, 

 gives rise to chromosomes 

 which lie scattered irregularly 

 through the nucleus (Figure 

 2). We have not as yet suc- 

 ceeded in determining the 

 exact number of the chromo- 

 somes, but believe that it is 

 not less than sixteen. The 

 nucleus now elongates, finally 

 becoming more or less spindle 

 shaped, but apparently fails 

 to reach the proximal pole of 

 the cell. Intranuclear spindle 

 fibres staining in iron haema- 

 toxylin have meanwhile made their appearance, extending from the 

 chromosomes first to the distal centrosome, and later in the opposite 

 direction, to a region near the proximal end of the nucleus, it being 

 now difficult to determine the exact extent of the nuclear membrane. 

 Thus the proximal ends of the spindle fibres often appear to converge to 

 a point at some distance from the corresponding centrosome (Figure 



Figures 1-4. Primary spermatocytes. X 

 2800. 



Figure 1. The two centrosomes moving 

 apart ; x, interzonal l)oi\y. 



Figure 2. Centrosomes at opposite poles 

 of cell ; nucleus showing chromosomes ; prx., 

 proximal centrosome; (ht., distal centrosome. 



Figure 3. First spindle figure with intra- 

 nuclear spindle fibres. 



Figure 4. Interzonal body at proximal 

 pole, immediately before its abstriction ; 

 spindle figure disappearing, and extranuclear 

 fibres j^rominent. 



